1. Technical Field
The present invention relates to a design method and a manufacture method of a spectacle lens performed according to a personal visual action.
2. Related Art
A person has his/her own way of seeing an object. For example, when seeing the side or the upper or lower region of the person, he or she rotates the head or the eyes (hereinafter referred to as visual action). The rotation angles of the head and the eyes are peculiar to the person, and thus various spectacle lens design methods capable of coping with individual visual actions variable for each person have been proposed (for example, see JP-T-2008-521027 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application), JP-T-2008-511033, JP-A-2007-256957, JP-A-2007-241276, and JP-T-2003-523244).
According to the technologies disclosed in the above references, a lens is designed according to personal visual action. However, these technologies give no consideration to prismatic effect produced when an object is seen through a spectacle lens.
The power of the spectacle lens varies for each prescription or design, and the position at which an object is recognized changes whether the object is seen without lens or seen through spectacle lens due to the prismatic effect. For example, when the object is seen through a convex lens, the object is recognized in a region shifted toward the center of the lens from the direction in which the object actually exists. In case of a concave lens, however, the object is recognized in a region shifted toward the periphery of the lens from the direction in which the object actually exists.
Since the position at which the object is recognized varies due to the prismatic effect of the lens, the rotation angle of the head when the person sees the object through the spectacle lens is different from the rotation angle of the head when the person sees the object without lens. For example, when the object is seen through the convex lens, the rotation angle of the head is larger than that when the object is seen without lens. On the contrary, when the object is seen through the concave lens, the rotation angle of the head is smaller than that when the object is seen without lens. When the prescription of the lens for the left eye is different from that for the right eye, the rotation angle of the left eye is also different from that of the right eye at the time of rotation of the eyeballs for seeing the object. For reducing this difference, the head tends to be rotated through large angle.
As can be understood, a personal visual action is greatly related to the prismatic effect of the spectacle lens. Thus, according to the methods disclosed in the above references, accurate correspondence between the rotation angle of the head and the lens design is difficult to be established. Accordingly, a lens sufficiently comfortable and satisfactory for a user cannot be provided in some cases.